Copper and zinc oxide-based catalysts have been known for many years; they have been described as soon as 1933 by DODGE (US-A-1,908,696). In U.S. Pat. Nos. 3,388,972 , 3,546,140 and 3,790,505 , the US company C.C.I. describes the use of Cu, Zn, Al ternary compositions for the conversion at low temperature of carbon oxide (CO) and for the synthesis of methanol.
Various methods for preparing Cu, Zn, Al catalysts are especially described in U.S. Pat. Nos. 3,923,694 , 4,279,781, 4,596,782 and FR-A-2,352,588.
FR-A-2,352,588 describes the preparation of a catalyst through the mechanical mixing of 10 to 60% of copper oxide, 5 to 40% of zinc oxide and 30 to 70% of an aluminous cement, as well as the use of this catalyst for the conversion of the carbon oxide in order to produce hydrogen or methanol.
Apart from the catalyst described in FR-A-2,352,588, these catalysts are generally produced by a precipitation reaction between an acid solution containing for example the nitrates of the metals cited above and a basic solution containing for example an alkaline carbonate. The precipitation reaction, such as that which is for example described in U.S. Pat. No. 3,923,694, leads to obtaining hydrated precursors, at least partly crystallized, ccnsisting of at least three phases: a CuAlZn ternary phase, with (Cu+Zn)/Al=3 (atoms.atom-1), of the hydrotalcite type; a binary phase, the rosacite, which is a mixed copper and zinc hydroxycarbonate; and a copper hydroxycarbonate, the malachite, and possibly also other phases, such as for example the ZnAl.sub.2 O.sub.4 spinel described in U.S. Pat. No. 3,923,694. The consequence of the heterogeneousness of composition of these catalysts is relatively low activity, selectivity and stability, even though they initially contain a copper oxide that is well-dispersed, at least partly. Various publications, as for example F. TRIFIRO et al, Preparation of Catalysts III, p. 723-733, 1983, Elsevier Science Publishers (Amsterdam), give a detailed description of the simultaneous forming of these phases.
The preparation of copper-based catalysts obtained by the calcination of identified crystallized precursors, and more particularly of hydroxycarbonated phases obtained by co-precipitation, has been rarely described. U.S. Pat. No. 4,145,400 describes the preparation of CuZnAl catalysts, but said catalysts are prepared from only one crystallized monophase precursor, hydrotalcite. As for U.S. Pat. No. 4,596,782, it describes the preparation of a methanol synthesis catalyst from only one amorphous hydrated precursor with a very high homogeneity. On the other hand, the catalyst described in U.S. Pat. No. 4,436,833 is prepared from the mixture of a binary crystallized phase of formulation Cu.sub.2,2 Zn.sub.2,8 (OH).sub.16 (CO.sub.3).sub.2 and of aluminum hydroxyde. Lastly, U.S. Pat. No. 3,923,694 describes a sequential co-precipitation where a spinel precursor containing aluminum and zinc is first obtained, then a binary Cu-Zn compound is co-precipitated on this precursor. In numerous documents, for example U.S. Pat. No. 3,388,972, 3,546,140, FR-A-2,027,162, the alumina, which is the main component of the catalyst, is introduced in the oxide state or else in the hydroxyde state (U.S. Pat. No. 4,279,781).